Chemistry Worksheets - Chem 340, Fall 2013 Page 7
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193.43 The cycle involved in the operation of an internal combustion engine is called the Otto cycle.
Air can be considered to be the working substance and can be assumed to be a perfect gas. The
cycle consists of the following steps: (1) reversible adiabatic compression from A to B, (2)
reversible constant-volume pressure increase from B to C due to the combustion of a small
amount of fuel, (3) reversible adiabatic expansion from C to D, and (4) reversible and
constant-volume pressure decrease back to state A. Determine the change in entropy (of the
system and of the surroundings) for each step of the cycle and determine an expression for the
efficiency of the cycle, assuming that the heat is supplied in Step 2. Evaluate the efficiency for a
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compression ratio of 10:1. Assume that in state A, V = 4.00 dm
, p = 1.00 atm,
and T = 300 K, that V
= 10V
, p
/p
= 5, and that C
= 7/2 R.
A
B
C
B
p,m
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